Electrophotographic toner

ABSTRACT

This invention discloses electrophotogrpahic toners and the methods for their preparation. The electrophotographic toners contain resin and coloring agents as primary components. The resin is a non-crosslinked polymer of vinyl monomers or its mixtures, and has a number average molecular weight (Mn) of 2,000-15,000, a Z average molecular weight (Mz) of not less than 400,000 and Mz/Mn of 50-600. The electrophotographic toners exert an excellent fixing ability at high duplication speed or at lower temperatures.

FIELD OF THE INVENTION

The present invention relates to an electrophotographic toner for use inthe development of an electrostatic image in electrophotography,electrostatic recording, electrostatic printing and the like.

BACKGROUND OF THE TECHNIC

Still more increasing tendency of duplication speed has recently beenfound in the electrophotography due to the increase of information to betreated.

Consequently, the heat quantity transferred from hot fixing rolls totoner is less at high duplication speed than at low duplication speed. Aremarkable decrease in the surface temperature of fixing rolls is alsocaused by the heat removal to copying papers. Therefore the toner isrequired to be fixed at lower temperatures and also to be free fromoffset phenomenon at these fixing temperatures. In order to obtain asharp image, improvement of resin has been conducted with respect to hotmelt properties such as fixing ability at lower temperatures and offsetresistance, as well as electrostatic characteristics of the toner.

For example, several patents have been known. Japanese PatentPublication No. 6895/1980 discloses a method for providing a tonerhaving a good offset resistance by using a resin having a weightaveragemolecular weight/number average molecular weight ratio of 3.5-40 and anumber average molecular weight of 2,000-30,000. Japanese PatentLaid-open No. 144,446/1975 describes a method for improving the fixingability by adding a small amount of plasticizers such as phthalic aciddiester into a toner having a good blocking and offset resistance.Japanese Patent Laid-open No. 101,031/1974 discloses a method forextending the range of fixing temperatures by using a crosslinked resinand for employing a toner which is offset resistant even at relativelyhigh fixing temperatures. Besides patents are known as a countermeasurefor providing the high electrostatic charge characteristics for thetoner. For example, Japanese Patent Publication 40,183/1983 discloses amethod for using aliphatic unsaturated carboxylic acids such asmethacrylic acid as a component of the resin. Japanese Patent Laid-openNo. 93,457/1984 discloses a method for providing charge stabilitytogether with the high electrostatic charge characteristics by adding acharge control agent composed of metal containing dyestuff as a toneringredient.

Furthermore, Japanese Patent Laid-open No. 16,144/1981 relevant to U.S.Pat. No. 4,499,168 describes a method for providing a magnetic tonerwhich is excellent in the fixing ability and impact resistance byemploying the resin having the maximum value of molecular weight in aspecific molecular weight region.

As above mentioned, the heat quantity provided from the hot fixing rollsis less at the high duplication speed than at the low-duplication speed.A marked decrease in the surface temperature of fixing rolls is alsocaused by the heat removal to the copying papers. Therefore it isnecessary fixing with a smaller quantity of heat. Smaller moleculeshaving lower glass transition temperature (hereinafter abbreviated asTg) are required for melting with low calory. Excess lowering of Tg,however, causes blocking and there is naturally a lower limit for theTg. The smaller molecules are assumed to reduce their melt viscositymore rapidly, enhance flowability of the resin at lower temperatures,and improve the fixing ability. Too small molecules, however, lead tolowering of Tg and occurrence of blocking problems.

On the other hand, as a result of increase in the duplication speed andnumbers of copying papers, the duplicated images are expected to havethe same quality from the 1 st to the dozens of thousandth sheet inaddition to have a sharp image and perfect fixation of the toner to thepaper.

Conventional methods for the improvement of offset resistance and lowtemperature fixation are related to the problems occurring afteradhesion of the toner to the paper. These methods are important and yetnot considered upon the requirement for adhering the toner in advance oneach copying paper uniformly and at a constant concentration. Theelectrostatic charge characteristics of the toner is an important factorfor the determination of toner quantity adhering on the paper andcontrols the image concentration. On the other hand, in the twocomponent type developers for example, triboelectrostatic chargegenerates by the friction of the toner with carrier. Consequentlypartial destruction of the toner causes separation of resinparticulates, particulate powder of coloring agents such as carbonblack, or powder of its aggregates. These particulates are differentfrom the employed toner particles in diameter and shape, ratio of theresin to coloring agents, molecular weight caused by destruction of thebinder resin molecules etc. Thus these particulates exhibit differentbehavior on the electrostatic charge characteristics. Consequentlyscattering of the particulates, make a dirty mark in the copy machineand increase in the background concentration of image are generated asthe increase in numbers of copying papers. As a result, the duplicatedimage cannot be maintained in the same quality.

In addition, the particulates are absorbed on the carrier and result inthe variation of triboelectrostatic charge which leads to alter theimage concentration. Accordingly the consistent maintenance of aconstant image concentration cannot be achieved. Aforesaid JapanesePatent Laid-open No. 16,144/1981 describes that above mentioneddestruction of the toner results from the lack of hardness in the binderresin and defines to have the maximum value in a molecular weight regionof 10⁵ -2×10⁶. The correlation between presence of the maximum value andhardness is not clear. Furthermore the maximum value is not essentialfor preventing the destruction of toner even though the maximum valueexists in this molecular weight region.

On the other hand, the method of Japanese Patent Laid-open No.101,031/1974 is an effective technique for improving resin strength andyet may cause poor flowability in the melted stage by the hot rollersbecause crosslinked binder resin, that is, gel is contained in thetoner. Consequently, irregular gloss emerges on the duplicated image,particularly in the solid block parts of the duplicate, and remarkablydamages the quality of image.

The methods of Japanese Patent Publication No. 40,183/1983 and JapanesePatent Laid-open No. 93,457/1984 are considered excellent forcontrolling the quantity of electrostatic charge in the initial stage ofduplication. The toner, however, is not guaranteed for its strength atall and has not yet been solved the problem of its destruction caused byincrease in the numbers of copying papers.

DISCLOSURE OF THE INVENTION

The object of this invention is to provide an electrophotographic tonerwhich is excellent in the fixing ability under high speed or at lowertemperatures, capable of obtaining a sharp, clean and good image, andalso outstanding in the resistance against blocking and offset.

Another object of this invention is to provide a suitable method for thepreparation of the electrophotographic toner having aforesaid excellentproperties. More particularly, it is to provide a method for preparing atoner resin which is specified in number average molecular weight (Mn),Z average molecular weight (Mz) and Mz/Mn, by mixing high molecularweight polymer with low molecular weight polymer.

The aforementioned first object can be achieved by providing thefollowing electrophotographic toner. That is, the toner contains resinand a coloring agent as primary components, said resin is anoncrosslinked polymer of vinyl monomer or its mixture, and the resinhas a number average molecular weight (Mn) of 2,000-15,000, a Z averagemolecular weight (Mz) of not less than 400,000 and a ratio of the Zaverage molecular weight to the number average molecular weight, e.g.Mz/Mn, of 50-600.

The resin in the aforementioned toner is a mixture obtained by mixingthe high molecular weight polymer and the low molecular weight polymerin a state of solution. The high molecular weight polymer is preferablya polymer having the Z average molecular weight of not less than 400,000prepared by a two step polymerization of the vinyl monomer. In thetwo-step polymerization, the monomer is subjected to a bulkpolymerization to the conversion of 30-90% by weight and successivelyadded with a solvent and a polymerization initiator to continue thereaction by a solution polymerization.

The aforesaid second object can be achieved by providing the method forpreparing the toner resin having a number average molecular weight (Mn)of

2,000-15,000, a Z average molecular weight (Mz) of not less than400,000, and Mz/Mn of 50-600 which comprises mixing 30-70 parts byweight of a solid component of high molecular weight polymer obtained byheating a vinyl monomer at 60°-150° C., conducting a bulk polymerizationto a conversion of 30-90% by weight, successively adding a solvent toreduce the viscosity of reaction mixture and carrying out a solutionpolymerization at 60°-150° C., with 70-30 parts by weight of a solidcomponent of low molecular weight polymer obtained by polymerizing astyrene type vinyl monomer at 190°-230° C. in a state of solution, andfollowed by removing the solvent from the resulting mixture.

The present inventors have assumed that the aforesaid problems resultfrom the lack of resin viscosity in the hot kneading stage conductedunder melting of the coloring agent and the resin. The lack of viscosityis considered to cause poor dispersion of the coloring agent and itssecondary aggregates in the resin. Thus destruction is liable to occurthrough impact during the duplication in the neighborhood of interfacebetween the coloring agent and the resin. Consequently by increasing Mzand Mz/Mn of the resin, the toner has been found to reduce the variationof its electrostatic charge during the duplication to a level of 10% orless, provide images having always constant quality during theduplication and at the same time improve the offset resistanceremarkably. Besides a marked improvement in the fixing ability has alsobeen found by controlling Mn and Mz/Mn of the resin. Furthermore theresin obtained by mixing with the low molecular weight polymerpolymerized at high temperatures and performing the solvent removal, hasalso been found to significantly improve the fixing ability.

The noncrosslinked polymer in this invention refers to the polymer whichcan be dissolved in tetrahydrofuran (THF) and found no insolubleingredients. The polymer or the mixture of polymers employed in thisinvention is required to have a Mn range of 2,000-15,000 andparticularly preferred to have a range of 2,000-10,000 in order toprovide heat melting ability for the toner resin at lower temperatures.The Mn value of less than 2,000 leads to poor dispersion of the coloringagent due to the viscosity reduction during the kneading, whereas thatof exceeding 15,000 results in poor fixing ability.

Besides the Z average molecular weight is the most important factor.That is, Mz most suitably indicates the size and amount of the molecularweight in the tailing portion of higher molecular weight side and has alarge effect on the properties of toner. The greater value of Mz hasbeen found to enhance the resin strength, increase the viscosity duringthe hot kneading, improve the dispersibility of the coloring agent,reduce the variation of electrostatic charge during the duplication,maintain the image concentration more constantly during the duplicationand reduces so called fogging which is caused by the contamination ofimage substrates due to scattering troubles. In order to obtain thesefavorable effects, Mz is 400,000 and more, and preferably 500,000 andmore in particular.

Besides it is needed to be easy to melt at the temperature and to have ahigh viscosity in the hot kneading stage. In order to obtain goodmelting ability and increased melt viscosity, the ratio Mz/Mn is in therange of 50-600 and preferably 70-600 in particular. Such resin ispreferred because it has a molecular weight region broadly extendingfrom low polymers to ultra-high polymers which increase the value of Mz.The ratio Mz/Mn of less than 50 leads to poor hot-melting ability anddeteriorates all of the duplication characteristics. On the other hand,in consideration of improving the properties in the neighborhood of 600,the ratio Mz/Mn of exceeding 600 is also supposed to have similareffect, and yet it is difficult to prepare such resin.

The resin containing aforesaid high molecular weight polymer havinglarge Mz and low molecular weight polymer is generally prepared by thefollowing method. The solution polymerization is carried out at lowertemperatures with a reduced rate of polymerization in the presence ofsolvent and polymerization initiator to form the high molecular weightpolymer having large Z average molecular weight. The solutionpolymerization is further continued at high temperatures in the presenceof a large quantity of the polymerization initiator to obtain the resin.The method, however, requires a long reaction time and causes poorproductivity in order to obtain sufficient amount of the high molecularweight polymer by polymerizing at lower temperatures.

An example of more preferred methods includes a two step polymerizationmethod wherein the vinyl monomer is subjected to the bulk polymerizationat a temperature of 60°-140° C. to a high conversion, followed by addingthe solvent and the polymerization initiator, and conducting thesolution polymerization to prepare a mixture with the low molecularweight polymer.

Suspension polymerization or emulsion polymerization is generallycarried out in order to increase the molecular weight of polymers. Insuch methods, however, emulsifiers or dispersants used in thepolymerization are contained in both phases of water, the dispersingmedium, and polymer particles. Thus it is difficult to sufficientlyremove the emulsifiers or the dispersants. In addition it is also hardto make the amount of these removed impurities constant. Therefore, theeffect of environmental humidity is very large on such polymers whenthey are used as the toner resin, and the object of this inventioncannot be achieved. That is, the variation of electrostatic charge isdifficult to reduce during the continuous copying operation for manyhours and constant quality of the duplicate is difficult to obtain.

The method for increasing the ratio Mz/Mn without containing crosslinkedpolymers such as gel has been extensively examined by bulk and solutionpolymerization. Consequently the two step polymerization has beenconducted by polymerizing the vinyl monomer in bulk at a temperature of60°-140° C. to a conversion of 30-90% by weight, successively adding thesolvent and polymerization initiator and carrying out the solutionpolymerization. The resulting high molecular weight polymer having a Zaverage molecular weight of not less than 400,000 has been mixed withthe low molecular weight polymer in a solution. The resin compositionthus obtained has been found to be suitable for the purpose of thisinvention.

Examples of the vinyl monomers which may be used in the presentinvention include acrylate esters such as methyl acrylate, ethylacrylate, propyl acrylate, butyl acrylate, octyl acrylate, cyclohexylacrylate, lauryl acrylate, stearyl acrylate, benzyl acrylate, furfurylacrylate, tetrahydrofurfuryl acrylate, hydroxyethyl acrylate,hydroxybutyl acrylate, dimethylaminomethyl acrylate, dimethylaminoethylacrylate; methacrylate esters such as methyl methacrylate, ethylmethacrylate, propyl methacrylate, butyl methacrylate, octylmethacrylate, lauryl methacrylate, stearyl methacrylate, cyclohexylmethacrylate, benzyl methacrylate, furfuryl methacrylate,tetrahydrofurfuryl methacrylate, hydroxyethyl methacrylate,hydroxypropyl methacrylate, hydroxybutyl methacrylate,dimethylaminomethyl methacrylate, dimethylaminoethyl methacrylate;aromatic vinyl monomers such as styrene, vinyl toluene, α-methylstyrene, chlorostyrene; unsaturated dibasic acid dialkyl esters such asdibutyl maleate, dioctyl maleate, dibutyl fumarate, dioctyl fumarate;vinyl esters such as vinyl acetate, vinyl propionate; nitrogencontaining vinyl monomers such as acrylonitrile, methacrylonitrile;unsaturated carboxylic acids such as acrylic acid, methacrylic acid,cinnamic acid; unsaturated dicarboxylic acids such as maleic acid,maleic anhydride, fumaric acid, itaconic acid; and unsaturateddicarboxylic acid monoesters such as monomethyl maleate, monoethylmaleate, monobutyl maleate, monoctyl maleate, monomethyl fumarate,monoethyl fumarate, monobutyl fumarate, monoctyl furmarate;styrenesulfonic acid, acrylamide, methacrylamide, N-substitutedacrylamide, N-substituted methacrylamide, acrylamidepropanesulfonic acidand the like. These vinyl monomers may be used alone or in combinationof two or more. Among these monomers, particularly preferred areacrylate esters, methacrylate esters, styrene, dialkyl fumarates,acrylonitrile, methacrylic acid, cinnamic acid, fumaric acid monoesters,acrylamide and methacrylamide.

Besides in the method of this invention, styrene type vinyl monomerssuch as styrene, α-methylstyrene, o-, m- and p-methylstyrene,vinyltoluene and chlorostyrene may be used as a primary component andoptionally copolymerized with above mentioned vinyl monomers. Amongthese styrene type vinyl monomers, styrene alone and combinations ofstyrene, methacrylic acid and/or methyl methacrylate are preferred inparticular.

Upon preparation of the high molecular weight polymer from aforesaidvinyl monomers, the two step polymerization may be conducted bypolymerizing in bulk at a temperature of 60°-150° C. in the absence ofpolymerization initiator, successively adding the solvent andpolymerization initiator, and completing the reaction by the solutionpolymerization. Mz of the resulting polymer, however, depends largelyupon the conversion in the bulk polymerization. According to theexamination of the present inventors, a trace amount of thepolymerization initiator may optionally be added by portions at 60°-80°C. This procedure, however, takes many hours and causes poorproductivity. More preferable results can be obtained by conducting heatpolymerization at a temperature of 80°-150° C. in the absence ofpolymerization initiator.

The conversion in the bulk polymerization has given good results in therange of 30-90% by large Mz cannot be obtained from the conversion ofless than 30% by weight. When the conversion exceeds 90% by weight, theincrease in Mz is saturated and the polymer becomes hard to handle inthe actual production due to high viscosity.

The termination of bulk polymerization may also be achieved by coolingthe reaction mixture or by the addition of cold solvent. The solventwhich may be used in the successive solution polymerization includes,for example, aromatic hydrocarbons such as benzene, toluene,ethylbenzene, o-xylene, m-xylene, p-xylene and cumene. Thesehydrocarbons may be used alone or in combination. Molecular weightcontrol may also be performed by selecting other solvents.

The solution polymerization is normally carried out at a temperature of80°-150° C., and may also be conducted outside of this temperature rangein order to adjust the molecular weight. The solution polymerization isperformed by adding the uniform mixture of the polymerization initiatorand solvent continuously or by portions over 1-20 hours. The addition byportions enhances the variation of polymerization initiatorconcentration and leads to a poor reproducibility of the molecularweight. Therefore continuous addition is preferably used in thereaction. Any compound which may be usually used as the initiator ofradical polymerization may be employed for the polymerization initiatorof this invention.

Examples of the polymerization initiator include, azo compounds such as2,2'-azobisisobutyronitrile,2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile),2,2'-azobis(2,4-dimethylvaleronitrile),2,2'-azobis(2-methylbutyronitrile), dimethyl-2,2'-azobisisobutyrate,1,1'-azobis(1-cyclohexanecarbonitrile),2-(carbamoylazo)-isobutyronitrile, 2,2'-azobis(2,4,4-trimethylpentane),2-phenylazo-2,4-dimethyl-4-methoxyvaleronitrile,2,2'-azobis(2-methylpropane); ketone peroxides such as methyl ethylketone peroxide, acetylacetone peroxide, cyclohexanone peroxide;peroxyketals such as 1,1-bis-(t-butylperoxy)-3,3,5-trimethylcyclohexane,1,1-bis-(butylperoxy)cyclohexane, 2,2-bis(t-butylperoxy)butane;hydroperoxides such as t-butyl hydroperoxide, cumene hydroperoxide,1,1,3,3-tetramethylbutyl hydroperoxide; dialkyl peroxides such asdi-t-butyl peroxide, t-butyl cumyl peroxide, dicumyl peroxide,2,5-dimethyl-2,5-di(t-butylperoxy)hexane,α,α'-bis(t-butylperoxyisopropylbenzene); diacyl peroxides such asisobutyryl peroxide, octanoyl peroxide, decanoyl peroxide, lauroylperoxide, 3,5,5-trimethylhexanoyl peroxide, benzoyl peroxide, m-toluylperoxide; peroxydicarbonates such as diisopropyl peroxydicarbonate,di-2-ethylhexyl peroxydicarbonate, di-n-propyl peroxydicarbonate,di-2-ethoxyethyl peroxydicarbonate, dimethoxyisopropylperoxydicarbonate, di(3-methyl-3-methoxybutyl) peroxydicarbonate;sulfonyl peroxides such as acetylcyclohexylsulfonyl peroxide;peroxyesters such as t-butyl peroxyacetate, t-butyl peroxyisobutyrate,t-butyl peroxyneodecanoate, cumyl peroxyneododecanoate, t-butylperoxy-2-ethylhexanoate, t-butyl peroxylaurate, t-butyl peroxybenzoate,t-butyl peroxyisopropylcarbonate, di-t-butyl diperoxyisophthalate; andthe like.

The type and quantity of such polymerization initiator may be suitablyselected according to the reaction temperature and conversion of thebulk polymerization. The initiator is normally used in an amount of0.01-10 parts by weight per 100 parts by weight of the monomer employed.

The aforesaid method can prepare the high molecular weight polymer whichis soluble in solvents, free from the gel and has a high Mz. Inaddition, ultra-high molecular weight polymer can be obtained by the useof a divinyl compound. That is, at the termination of bulkpolymerization or in the solution polymerization stage, the divinylcompound is added in an amount of 0.01-1 part by weight per 100 parts byweight of the total amount of monomer used. The reaction can increase Mzof the intact solvent soluble polymer without accompanyingthree-dimensional cross-linking reaction by the divinyl compound. Thedivinyl compound which may be employed in this invention is capable ofcopolymerizing with the above-mentioned ethylenically unsaturatedmonomer. Examples of the divinyl compound include divinylbenzene,(poly)-ethylene glycol diacrylate and (poly)ethylene glycoldimethacrylate. The greater amount in use leads to higher effect on theMz increase, and yet it is undesirable to use more than 1 part by weightbecause gel like insoluble matter is found.

An alternative method for further increasing Mz is to use methacrylicacid in an amount of 1-15 parts by weight in 100 parts by weight of theethylenically unsaturated monomer employed. Methacrylic acid is requiredto undergo the bulk polymerization in the absence of the catalyst. Whenmethacrylic acid is added after completion of the bulk polymerizationwithout methacrylic acid, the increase in Mz cannot be found in thesuccessive solution polymerization. Unsaturated monomers other thanmethacrylic acid, for example, acrylic acid, maleic acid, monoalkylmaleate, fumaric acid and monoalkyl fumarate lead to insolubilization ofthe resulting polymer or exert no effect, and hence methacrylic acid isrequired. Methacrylic acid is used in an amount of 1-15 parts by weight.The effect on Mz increase is small in an amount less than 1 part byweight while an amount exceeding 15 parts by weight is unfavorablebecause of separation of the solvent insoluble matter.

Any high molecular weight polymer thus obtained has a Mz of more than400,000 and its melt viscosity is high enough to hot kneading in thetoner preparation stage. Easiness of hot melting, however, is alsorequired in order to achieve low energy fixation at the same time. Thepresent inventors have found more preferable method for solving theseproblems. In this method, the high molecular weight polymer obtainedabove and having a large Mz is mixed in a state of solution with the lowmolecular

weight polymer having Mn of 1,000-5,000 so that the resulting mixturehas Mn of 2,000-10,000 and Mz/Mn of 50-600.

The solution polymerization method capable of remarkably reducing thecontent of impurity is preferably used for preparing the low molecularweight polymer. The molecular weight may be suitably controlled bysolvent/monomer ratio, sort of the solvent, use of a chain transferagent, quantity and sort of the radical polymerization initiator,reaction temperature etc. Any of above illustrated monomer may be usedfor the solution polymerization.

In order to obtain heat-melting ability of the toner resin compositionat lower temperatures, the low molecular weight polymer is favorablyprepared by polymerizing the vinyl monomer in solution at a temperatureof 190°-230° C. The resulting polymer has preferably a glass transitiontemperature of 40°-75° C. and a number average molecular weight of1,000-5,000, particularly 1,500-2,800. The polymerization temperature ofless than 190° C. is unpreferable because the low molecular weightpolymer cannot be obtained and the fixing ability of the toner becomespoor. The polymerization temperature of exceeding 230° C. is alsoundesirable because by-product oligomer, apparently the thermal reactionproduct of the monomer, is generated in a relatively large amount andthe blocking resistance of the toner reduces. Even at a polymerizationtemperature of less than 190° C., low molecular weight polymer can beobtained by using a large amount of the polymerization initiator,solvent or chain transfer agent. On the other hand, a large quantity ofresidue of polymerization initiator is difficult to eliminate in thesolvent removal and liable to cause variation of the triboelectrostaticcharge. The solvent also causes a marked reduction of productivity by anabundant use. A large amount use of the chain transfer agent isundesirable because of odor or corrosion problems. Therefore the lowmolecular weight polymer obtained by using a small amount of thepolymerization initiator and a higher reaction temperature is preferablefor preparing the electrostatically stable toner resin composition.

The mixing ratio of the high molecular weight polymer to the lowmolecular weight polymer which may be used in this invention is 30-70parts by weight of the former as solid and 70-30 parts by weight of thelatter as solid. The high molecular weight polymer in a ratio of lessthan 30 parts by weight fails to provide sufficiently large Mz, causesunsatisfactory dispersion of the coloring agent, leads to a largevariation in the electrostatic charge, and at the same time results inan insufficient offset resistance. On the contrary, the high molecularweight polymer in a ratio of larger than 70 parts by weight causes amarked reduction of hot-melting and fixing properties. Besides the highmolecular weight polymer and the low molecular weight polymer may bemixed with, for example, a stirrer in the form of solutions respectivelydissolved in the same or the mutually compatible solvent. The resultingmixture is heated to a high temperature and flashed in a vacuum system,thereby the solvent, unreacted monomer, residue of polymerizationinitiator etc. are rapidly evaporated, foamed and removed. At the sametime the polymers are further mixed to give a homogeneous mixture.

The toner which may be used in this invention is mainly a powdery drytoner. Its principal component, that is, the aforesaid polymer mixtureis required to be solid at the room temperature and also to be free fromcaking after standing for many hours. According to such point of view,the glass transition point of the above-mentioned polymer mixture ispreferably not less than 40° C. and more preferably not less than 50° C.In addition, according to the viewpoint of the lower temperature fixingability, the polymer mixture is preferred to soften at lowertemperatures as possible. Thus the glass transition temperature of thepolymer mixture is preferably not more than 90° C., and more preferablynot more than 80° C.

In the practice of this invention, the below described ingredients mayoptionally be added to the resin so long as they are harmless to theeffect of this invention. The resin which may be used as a part of thisinvention includes, for example, polyvinyl chloride, polyvinyl acetate,polyolefin, polyester, polyvinylbutyral, polyurethane, polyamide, rosin,modified rosin, terpene resin, phenol resin, aliphatic hydrocarbonresin, aromatic petroleum resin, paraffin wax and polyolefin wax.

Examples of the coloring agent which may be used in this inventioninclude black pigments such as carbon black, acetylene black, lampblack, magnetite, and known organic and inorganic pigments such aschrome yellow, iron oxide yellow, Hansa yellow G, quinoline yellow lake,permanent yellow NCG, molybdene orange, vulcan orange, indanthrene,brilliant orange GK, iron oxide red, brilliant carmine 6B, flizarinlake, methyl violet lake, fast violet B, cobalt blue, alkali blue lake,phthalocyanine blue, fast sky blue, pigment green B, malachite greenlake, titanium dioxide and zinc white. These ingredients are added

normally in an amount of 5-250 parts by weight per 100 parts by weightof the resin.

The toner composition of this invention may be selectively added withknown charge control agent, such as nigrosine and metal containing azodyestuff, pigment dispersant and offset inhibitors. The toner may beprepared by known methods. That is, the resin composition which haspreviously been added with aforesaid various ingredients is premixed ina powdery state and kneaded in a hot-melted stage by use of processingmachines such as hot rolls, Banbury mixer, extruder etc. After coolingthe resulting mass, it is finely ground with a pulverizing mill andsubjected to classification with an air classifier. The particles havingdiameters ranging normally 8-20 μm are collected to prepare the toner.

EXAMPLE

The present invention will further be illustrated in detail with respectto the following examples. Unless otherwise explained practically, theunit is part by weight or percent by weight.

Z average molecular weight (Mz), weight average molecular weight (Mw)and number average molecular weight (Mn) were determined by thefollowing conditions in accordance with GPC.

GPC equipment: JASCO TWINCLE HPLC

Detector: SHODEX R1-SE-31

Column: SHODEX GPCA-80MX2+xF-802X1

Solvent: Tetrahydrofuran (THF)

Flow rate: 1.2 ml/min

Sample: 0.25% THF solution

Furthermore duplication characteristics were measured under thefollowing conditions by Electrophotographic Copying Machine EP870 (aproduct from Minolta Camera Co.) equipped with Teflon hot-rolls. Fixingability:

A plastic eraser "MONO" (a product from Tombo Pencil Co.) was gone backand forth 20 times with a constant force between a solid black part anda non-tonered white part on a duplicated sheet. Toner removal from theblack part and soil of the white part were observed and divided into thefollowing four classes.

⊚ . . . No toner removal at all.

∘ . . . Good.

Δ . . . Toner was somewhat removed.

X . . . Poor. Toner was removed and caused much soil.

Contamination of the white background

The white part of the 100th sheet was compared with that of the 10,000thsheet in a continuous copying operation. The degree of contamination onthe white background due to the scattering of toner was divided into thefollowing three classes.

◯ . . . Good.

Δ . . . Contamination was observed with a magnifying glass having amagnification of 30 times.

X . . . Contamination was observed with the naked eye.

Offset resistance

The offset refers to a phenomenon that a part of the toner is attachedon the surface of a fixing roll and then transferred again onto thefresh surface of a paper after one rotation of the roll to cause thecontamination of the paper.

◯ . . . No contamination was found over 10,000 sheets of continuouscopying operation.

X . . . Contamination was found in the same conditions.

Variation of electrostatic charge

In the continuous copying operation, triboelectrostatic charges of the100th and 10,000th duplicates were expressed by the following ratio(absolute value). ##EQU1##

When the ratio was not more than 10(%), the variation was consideredgood. Dispersibility of the coloring agent:

A slide glass was put on a hot plate previously heated at 250°-300° C.and a small amount of the toner was placed on the slide glass. A coverglass was put on the toner sample simultaneously with the fusion of thetoner and pressed with a given pressure for 60 seconds. The sample wastaken out of the hot plate and allowed to cool. The dispersibility ofcoloring agent was observed with an optical transmission microscopehaving a magnification of 400-1,000 times.

The results of the observation was divided into the following twoclasses.

◯ . . . No undispersed or aggregated particles of the coloring agentwere found in any field of vision.

X . . . Many undispersed or aggregated particles of the coloring agentwere found.

Reproducibility of the completely solid black part

Irregular glass of the solid black part was observed on the 100thduplicate from the start of copying operation. The results were dividedinto the following three classes.

◯ . . . Irregular gloss was slight.

Δ . . . Irregular gloss was found in some degree.

X . . . Irregular gloss was remarkable.

Blocking resistance

Blocking resistance was evaluated by observing the aggregation afterallowing to stand the toner for hours at the temperature of 55° C. under80% relative humidity. Results were illustrated by the following fourclasses.

⊚ . . . No aggregation was found at all.

◯ . . . Aggregation was found partially but easily unfastened.

Δ . . . Firm coagulate was found in part.

X . . . Firm coagulate was found entirely.

PREPARATION EXAMPLE 1

A flask was flushed with nitrogen and charged with 60 parts of styreneand 40 parts of butyl methacrylate as monomers. The mixture was heatedin an oil bath and polymerized in bulk for 3 hours by maintaining thereaction temperature at 130° C. A conversion of 35% was obtained by thebulk polymerization in the absence of polymerization initiator. In thenext step, 120 parts of xylene were added and the resulting solution wascontinuously added over 10 hours with a solution obtained by dissolving1 part of azobisisobutyronitrile (AIBN) in 80 parts of xylene whilemaintaining the reaction temperature at 100° C. The polymerization wascompleted after continuing the reaction for further 2 hours. Theresulting polymer was named H-1 and the results are illustrated inTable-1.

PREPARATION EXAMPLE 2

Polymers were obtained by carrying out the same procedures as inPreparation Example 1 except the reaction time of bulk polymerizationwas extended so as to obtain conversion of 50%, 70% and 85%. Theresulting polymers were called H-2, H-3 and H-4 respectively and theresults are illustrated in Table-1.

COMPARATIVE PREPARATION EXAMPLE 1

Polymer was obtained by conducting the same procedures as in PreparationExample 1 except the reaction time of bulk polymerization was reduced toobtain conversion of 20%, and a solution obtained by dissolving 1 partof AIBN and 1 part of divinylbenzene in 80 parts of xylene was added inthe second step. The resulting polymer was named C-1 and the results areillustrated in Table-1.

COMPARATIVE PREPARATION EXAMPLE 2

In Preparation Example 1, 0.2 part of AIBN was added to the monomers andthe bulk polymerization was conducted for 2 hours while maintaining thereaction temperature at 100° C. The resulting conversion was 44%. In thenext-step, the same procedures as in Preparation Example 1 was carriedout to obtain the polymer C-2. The results are illustrated in Table-1.

PREPARATION EXAMPLE 3

The polymer H-5 was obtained by conducting the same procedures as inPreparation Example 1 except 0.6 part of divinylbenzene was added afteradding 120 parts of xylene in the second step. The results areillustrated in Table-1.

PREPARATION EXAMPLE 4

The polymer H-6 was obtained by conducting the same procedures as inPreparation Example 1 except the solution consisting of 1 part of AIBNand 80 parts of xylene was added with 0.6 part of divinylbenzene. Theresults are illustrated in Table-1.

COMPARATIVE PREPARATION EXAMPLE 3

The polymer C-3 was obtained by conducting the same procedures as inPreparation Example 4 except 1.5 parts of divinylbenzene were added. Theresults are illustrated in Table-1.

PREPARATION EXAMPLE 5

The polymer H-7 was obtained by conducting the same procedures as inPreparation Example 1 except 60 parts of styrene, 30 parts of butylacrylate and 10 parts of methacrylic acid were used as the monomers. Theresults are illustrated in Table-1.

COMPARATIVE PREPARATION EXAMPLE 4

The polymer C-4 was obtained by conducting the same procedures as inPreparation Example 5 except 50 parts of styrene and 20 parts ofmethacrylic acid were used. The results are illustrated in Table-1.

COMPARATIVE PREPARATION EXAMPLE 5

The polymer C-5 was obtained by conducting the same procedure as inPreparation Example 5 except acrylic acid was used in place ofmethacrylic acid. The results are illustrated in Table-1.

PREPARATION EXAMPLE 6

The polymer H-8 was obtained by conducting the same procedure as inPreparation Example 1 except 70 parts of styrene, 28 parts of butylacrylate and 2 parts of methacrylic acid were used as the monomers. Theresults are illustrated in Table-1.

PREPARATION EXAMPLE 7

Bulk polymerization was carried out at 130° C. for 4 hours by using 68parts of styrene, 27 parts of butyl acrylate and 5 parts of methacrylicacid as monomers. Polymerization ratio obtained was 41% in the bulkpolymerization. In the next step, 60 parts of xylene were added. Theresulting solution was added with 0.3 part of tetraethyleneglycoldiacrylate and then continuously added over 3 hours with a solutionobtained by dissolving 5 parts of AIBN in 200 parts of xylene whilemaintaining the reaction temperature at 120° C. The polymerization wascompleted after containing the reaction for further 3 hours to obtainpolymer H-9. The results are illustrated in Table-1.

COMPARATIVE PREPARATION EXAMPLE 6

The bulk polymerization was conducted at 120° C. for 2 hours by using 60parts of styrene and 40 parts of butyl methacrylate as monomers.Conversion obtained in the bulk polymerization was 18%. In the nextstep, 75 parts of xylene were added. The resulting solution was addedwith 1.5 parts of AIBN over 8 hours by 5 portions at every 2 hours whilemaintaining the reaction temperature at 90° C. The polymer C-6 wasobtained after completing the polymerization. The results areillustrated in Table-1.

PREPARATION EXAMPLE 8 (Example for the preparation of low molecularweight polymer)

A flask was charged with 100 parts of xylene or a solvent mixture ofxylene and cumene and heated to 120°-155° C. The mixture wascontinuously added dropwise over 5 hours with a solution consisting of90 parts of styrene, 10 parts of butyl acrylate and 1-5 parts of AIBN.

The polymers L-1-L-3 having different Mn were obtained after continuingthe polymerization for further 2 hours.

EXAMPLE 1 (Preparation of the toner resin)

The above-mentioned H-1˜H-9, C-1˜C-6 and L-1˜L-3 were mixed as such orafter dissolving in solvents. The mixture was heated, subjected tosolvent removal under vacuum and cooled. The resulting mass waspulverized so as to obtain a size of 3 mm and less. The resin D-1≠D-29were thus obtained.

(Preparation of the toner)

In a Henshel mixer, 100 parts of the resin, 10 parts of carbon black(MA-100: a product from Mitsubishi Chemical Co.) as a coloring agent, 3parts of polypropylene wax and 0.5-2 parts of Spiron Black TRH as acharge control agent were mixed. The mixture was hot-kneaded with a twinscrew extruder at a temperature of 140° C. (inlet)-150° C. (outlet),cooled and crushed. The resulting mass was finely ground with a jet milland subjected to air classification to obtain the toner having aparticle size of 8-20 μm (11.5 μm in average). The resulting toner wasmixed with 0.15 part of colloidal silica in a Henshel mixer and tested.

The amount of charge control agent was controlled to obtain -15 μC/g ofblow off electrostatic charge after mixing 95 parts of the carrier forEP870 with 5 parts of the toner in a V-blender for 30 minutes.

The test results of above-described toner are illustrated in Table-2.These results clearly illustrate that the toner of this invention exertsvery excellent duplication characteristics.

Equations for calculating molecular weights are illustrated below. Themolecular weights described in this invention are respectively definedas follows, provided that Ni molecules having a molecular weight of Miare present in an unit volume.

(1) Number average molecular weight Mn= ##EQU2## (2) Weight averagemolecular weight Mw= ##EQU3## (3) Z average molecular weight Mz=##EQU4##

                                      TABLE 1                                     __________________________________________________________________________                Monomer                      Bulk                                                  Butyl  Butyl                                                                              Methacrylic                                                                          Acrylic                                                                            polymerization                       Example                                                                              Polymer                                                                            Styrene                                                                            methacrylate                                                                         acrylate                                                                           acid   acid Initiator                                                                          Conversion                      __________________________________________________________________________    P. Ex-1 (1)                                                                          H-1  60   40                      0    35                              P. Ex-2                                                                              H-2  60   40                      0    50                                     H-3  60   40                      0    70                                     H-4  60   40                      0    85                              C. P. Ex-1 (2)                                                                       C-1  60   40                      0    20                              C. P. Ex-2                                                                           C-2  60   40                        0.2                                                                              44                              C. P. Ex-3                                                                           H-5  60   40                      0    35                              C. P. Ex-4                                                                           H-6  60   40                      0    35                              C. P. Ex-3                                                                           C-3  60   40                      0    35                              P. Ex-5                                                                              H-7  60          30   10          0    33                              C. P. Ex-4                                                                           C-4  50          30   20          0    31                              C. P. Ex-5                                                                           C-5  60          30          10   0    35                              P. Ex-6                                                                              H-8  70          28    2          0    34                              P. Ex-7                                                                              H-9  68          27    5          0    41                              C. P. Ex-6                                                                           C-6  60   40                      0    18                              P. Ex-8                                                                              L-1  90          10               --   --                                     L-2  90          10               --   --                                     L-3  90          10               --   --                              __________________________________________________________________________                          Molecular weight                                               Divinyl compound                                                                             Mz ×                                                                         Mw ×                                                                        Mn ×      Insoluble                      Example                                                                              Name      Amount                                                                             10.sup.4                                                                           10.sup.4                                                                          10.sup.4                                                                           Mz/Mn                                                                              Mw/Mn matter                         __________________________________________________________________________    P. Ex-1 (1)           45.5 19.0                                                                              2.4  19.0  7.9  No.                            P. Ex-2               68.6 41.4                                                                              3.3  20.8 12.5  "                                                    75.4 44.0                                                                              3.1  24.3 14.2  "                                                    83.4 50.9                                                                              14.4  5.8  3.5  "                              C. P. Ex-1 (2)                                                                       Divinyl-  1    38.3 15.7                                                                              1.2  31.9 13.1  "                                     benzene C. A. (3)                                                      C. P. Ex-2            32.2 10.2                                                                              1.0   3.2 10.2  "                              C. P. Ex-3                                                                           Divinyl-  0.6  68.5 29.2                                                                              2.5  27.3 11.7  "                                     benzene                                                                C. P. Ex-4                                                                           Divinyl-  0.6  94.5 56.4                                                                              2.1  45.0 26.9  "                                     benzene C. A.                                                          C. P. Ex-3                                                                           Divinyl-  1.5  (4) --                                                                             --  --   --   --    Present                               benzene C. A.                                                          P. Ex-5               84.8 38.0                                                                              1.5  56.5 25.3  No.                            C. P. Ex-4            (4) --                                                                             --  --   --   --    Present                        C. P. Ex-5            (4) --                                                                             --  --   --   --    Present                        P. Ex-6               69.5 41.4                                                                              3.3  21.1 12.5  "                              P. Ex-7                                                                              Tetraethylene                                                                           0.3  186.9                                                                              48.1                                                                              1.3  143.8                                                                              37.0  "                                     glycol                                                                        diacrylate                                                             C. P. Ex-6            26.6 12.5                                                                              3.0   8.9  4.2  "                              P. Ex-8          --    0.78                                                                               0.46                                                                              0.24                                                                               3.3  1.9                                                  --    2.21                                                                               1.2                                                                               0.41                                                                               5.4  2.9                                                  --   19.9  9.8                                                                              1.5  13.3  6.5                                 __________________________________________________________________________     Note:                                                                         (1) P. Ex . . . Preparation Example.                                          (2) C. P. Ex . . . Comparative Preparation Example                            (3) C. A. . . . Continuous Addition                                           (4) . . . unmeasured due to THF insoluble                                

                                      TABLE 2                                     __________________________________________________________________________            High molecular                                                                         Low molecular                                                                          Resine molecular weight                                     weight polymer                                                                         weight polymer                                                                         Mz ×                                                                        Mw ×                                                                        Mn ×                                  Resin   Name                                                                              Amount                                                                             Name                                                                              Amount                                                                             10.sup.4                                                                          10.sup.4                                                                          10.sup.4                                                                          Mz/Mn                                                                              Mw/Mn                              __________________________________________________________________________    Ex (1)                                                                             D-1                                                                              H-5 90   L-1 10   68.3                                                                              26.5                                                                              1.3  52.5                                                                              20.4                               Ex (1)                                                                             D-2                                                                              H-5 80   L-1 20   68.3                                                                              23.4                                                                              0.92                                                                               74.2                                                                              25.4                               Ex (1)                                                                             D-3                                                                              H-5 70   L-1 30   67.8                                                                              20.5                                                                              0.61                                                                              111.1                                                                              33.6                               Ex (1)                                                                             D-4                                                                              H-5 60   L-1 40   66.1                                                                              17.2                                                                              0.49                                                                              134.9                                                                              35.1                               Ex (1)                                                                             D-5                                                                              H-5 50   L-1 50   65.6                                                                              14.7                                                                              0.41                                                                              160.0                                                                              35.9                               Ex (1)                                                                             D-6                                                                              H-5 40   L-1 60   63.1                                                                              11.8                                                                              0.36                                                                              175.3                                                                              32.8                               Ex (1)                                                                             D-7                                                                              H-5 30   L-1 70   52.6                                                                               8.3                                                                              0.32                                                                              164.4                                                                              25.9                               C. Ex (2)                                                                          D-8                                                                              H-5 20   L-1 80   39.3                                                                               4.9                                                                              0.29                                                                              135.5                                                                              16.9                               C. Ex (2)                                                                          D-9                                                                              H-5 100  --  --   68.5                                                                              29.2                                                                              2.5  27.3                                                                              11.7                               Ex   D-10                                                                             H-9 100  --  --   186.9                                                                             48.1                                                                              1.3 143.8                                                                              37.0                               "    D-11                                                                             H-9 40   L-1 60   176.3                                                                             19.5                                                                              0.30                                                                              587.7                                                                              65.0                               "    D-12                                                                             H-1 50   L-2 50   45.2                                                                               9.8                                                                              0.69                                                                               65.5                                                                              14.2                               "    D-13                                                                             H-2 50   L-2 50   66.2                                                                              20.5                                                                              0.73                                                                               90.7                                                                              28.1                               "    D-14                                                                             H-3 50   L-2 50   73.4                                                                              21.5                                                                              0.70                                                                              104.5                                                                              30.7                               "    D-15                                                                             H-4 50   L-2 50   81.8                                                                              26.9                                                                              0.81                                                                              101.0                                                                              33.2                               C. Ex                                                                              D-27                                                                             H-4 80   L-2 20   82.3                                                                              42.3                                                                              1.8  45.7                                                                              23.5                               Ex   D-28                                                                             H-4 70   L-2 30   82.2                                                                              37.1                                                                              1.3  63.2                                                                              28.5                               C. Ex                                                                              D-16                                                                             C-1 50   L-2 50   36.5                                                                               8.3                                                                              0.63                                                                               57.9                                                                              13.2                               "    D-17                                                                             C-2 50   L-2 50   28.6                                                                               5.6                                                                              0.59                                                                               48.5                                                                               9.5                               "    D-18                                                                             H-2 50   L-3 50   68.2                                                                              26.3                                                                              2.2  31.0                                                                              12.0                               "    D-19                                                                             C-3 50   L-2 50   (3) --                                                                            --  --  --   --                                 "    D-20                                                                             C-5 50   L-2 50   (3) --                                                                            --  --  --   --                                 Ex   D-21                                                                             H-6 50   L-2 50   94.2                                                                              29.5                                                                              0.66                                                                              142.7                                                                              44.7                               "    D-22                                                                             H-7 50   L-2 50   84.6                                                                              19.9                                                                              0.63                                                                              132.3                                                                              31.6                               "    D-23                                                                             H-8 50   L-2 50   68.9                                                                              22.1                                                                              0.74                                                                               93.1                                                                              29.9                               C. Ex                                                                              D-24                                                                             C-4 50   L-2 50   (3) --                                                                            --  --  --   --                                 "    D-25                                                                             C-6 50   L-2 50   23.2                                                                               6.7                                                                              0.73                                                                               31.8                                                                               9.2                               "    D-26                                                                             --  --   L-3 50   19.9                                                                               9.8                                                                              1.5  13.3                                                                               6.5                               Ex   D-29                                                                             H-9 50   L-2 50   181.6                                                                             25.4                                                                              0.61                                                                              297.7                                                                              41.6                               __________________________________________________________________________               Duplication characteristics                                                   Fixing          Charge Color                                       Resin      ability                                                                           Contamination                                                                         Offset                                                                            variation (%)                                                                        dispersion                                                                          Reproducibility                       __________________________________________________________________________    Ex (1)  D-1                                                                              ◯˜Δ                                                       ◯                                                                         ◯                                                                     5.7    ◯                                                                       ◯˜Δ           Ex (1)  D-2                                                                              ◯                                                                     ◯                                                                         ◯                                                                     5.2    ◯                                                                       ◯                         Ex (1)  D-3                                                                              ◯                                                                     ◯                                                                         ◯                                                                     5.5    ◯                                                                       ◯                         Ex (1)  D-4                                                                              ⊚                                                                  ◯                                                                         ◯                                                                     5.2    ◯                                                                       ◯                         Ex (1)  D-5                                                                              ⊚                                                                  ◯                                                                         ◯                                                                     5.5    ◯                                                                       ◯                         Ex (1)  D-6                                                                              ⊚                                                                  ◯                                                                         ◯                                                                     4.8    ◯                                                                       ◯                         Ex (1)  D-7                                                                              ⊚                                                                  ◯                                                                         ◯                                                                     7.0    ◯                                                                       ◯                         C. Ex (2)                                                                             D-8                                                                              ◯                                                                     Δ ◯                                                                     12.1   Δ                                                                             ◯                         C. Ex (2)                                                                             D-9                                                                              X   X       X   15.2   X     Δ                               Ex      D-10                                                                             ◯                                                                     ◯                                                                         ◯                                                                     3.2    ◯                                                                       ◯˜Δ           "       D-11                                                                             ⊚                                                                  ◯                                                                         ◯                                                                     2.3    ◯                                                                       ◯                         "       D-12                                                                             ◯                                                                     ◯                                                                         ◯                                                                     9.5    ◯                                                                       ◯                         "       D-13                                                                             ⊚                                                                  ◯                                                                         ◯                                                                     5.3    ◯                                                                       ◯                         "       D-14                                                                             ⊚                                                                  ◯                                                                         ◯                                                                     4.2    ◯                                                                       ◯                         "       D-15                                                                             ⊚                                                                  ◯                                                                         ◯                                                                     4.1    ◯                                                                       ◯                         C. Ex   D-27                                                                             X   Δ˜X                                                                       Δ                                                                           11.5   Δ                                                                             Δ                               Ex      D-28                                                                             ◯˜Δ                                                       ◯                                                                         ◯                                                                     6.0    ◯                                                                       ◯˜Δ           C. Ex   D-16                                                                             ◯˜Δ                                                       Δ ◯                                                                     11.5   Δ                                                                             ◯                         "       D-17                                                                             X   X       Δ                                                                           24.3   X     ◯                         "       D-18                                                                             X   ◯                                                                         X   17.0   X     Δ                               "       D-19                                                                             ◯                                                                     Δ ◯                                                                     14.3   Δ                                                                             X                                     "       D-20                                                                             ◯                                                                     Δ ◯                                                                     20.6   Δ                                                                             X                                     Ex      D-21                                                                             ⊚                                                                  ◯                                                                         ◯                                                                     4.3    ◯                                                                       ◯                         "       D-22                                                                             ⊚                                                                  ◯                                                                         ◯                                                                     6.1    ◯                                                                       ◯                         "       D-23                                                                             ⊚                                                                  ◯                                                                         ◯                                                                     7.1    ◯                                                                       ◯                         C. Ex   D-24                                                                             ⊚                                                                  ◯                                                                         ◯                                                                     11.6   Δ                                                                             Δ˜X                       "       D-25                                                                             X   X       X   16.2   X     ◯                         "       D-26                                                                             Δ˜X                                                                   X       X   31.3   X     ◯˜Δ           Ex      D-29                                                                             ⊚                                                                  ◯                                                                         ◯                                                                     3.1    ◯                                                                       ◯                         __________________________________________________________________________     Note:                                                                         (1) Ex . . . Example                                                          (2) C. Ex . . . Comparative Example                                           (3) GPC unmeasured                                                       

EXAMPLE 2

A flask was flushed with nitrogen and charged with 72 parts of styreneand 28 parts of butyl acrylate as vinyl monomers. The mixture was heatedto 120° C. and polymerized in bulk for 10 hours at the temperature. Theconversion obtained was 55%. In the next step, 30 parts of xylene wasadded and the resulting solution was continuously added over 8 hourswith a solution obtained by dissolving 0.1 part of dibutyl peroxide in50 parts of xylene while maintaining the reaction temperature at 130° C.The polymerization was completed after continuing the reaction forfurther an hour. The resulting high molecular weight polymer was namedA-1.

In the next step, solution polymerization was conducted by continuouslyadding a homogeneous solution of 0.5 mole of di-t-butyl peroxide in 100moles of styrene at a rate of 750 ml/hr to the mixture consisting of 70parts of styrene and 30 parts of a solvent mixture containing xylene andethylbenzene. The reaction conditions maintained were an internalreactor temperature of 210° C., the internal pressure of 6 Kg/cm² and anoutlet temperature of 100° C.

The resulting low molecular weight styrene polymer had a conversion of99.5% by weight. The molecular weight was measured in accordance withgel permeation chromatography by using monodispersed standardpolystyrene as a reference sample and tetrahydrofuran as an eluent. Thenumber average molecular weight thus obtained was 2,100.

Besides the solid polymer A-2 was obtained by removing the solvent andits Tg was measured with a differential scanning calorimeter by usingalumina as reference. The measured Tg was 70° C.

A mixture was prepared from 50 parts of the above low molecular weightstyrene polymer A-2 and 90 parts of the aforesaid high molecular weightpolymer A-1 (50 parts as solid). The solvent was removed from themixture by heating to 200° C. and flashing into a vacuum system of 10mmHg. The resulting polymer had Mn of 2,800, Mz of 652,000, Mz/Mn of 233and Tg of 57° C.

EXAMPLE 3-4

A mixture of low molecular weight and high molecular weight polymerswere prepared by conducting the same procedures as in Example 2 exceptthe low molecular weight styrene polymer was polymerized at 190° C. and230° C. The molecular weights and Tg of the resultant polymer mixtureare illustrated in Table-3.

COMPARATIVE EXAMPLES 1-2

A mixture of low molecular weight and high molecular weight polymerswere prepared by conducting the same procedures as in Example 2 exceptthe low molecular weight styrene polymer was polymerized at 170° C. and240° C. The molecular weights and Tg of the resultant polymer mixtureare illustrated in Table-3.

EXAMPLE 5

A flask was charged with 100 parts of xylene and refluxed at about 140°C. A mixture of 90 parts of styrene, 10 parts of butyl acrylate and 8parts of AIBN was continuously added dropwise over 10 hours. Thepolymerization was continued for further 2 hours to obtain low molecularweight polymer. Then the solvent was removed to obtain the solid lowmolecular weight polymer B-2.

A mixture of low molecular weight and high molecular weight polymerswere prepared by conducting the same procedures as in Example 2 exceptthe above obtained low molecular weight polymer B-2 was used in place ofthe low molecular weight polymer A-2. The molecular weights and Tg ofthe resulting polymer mixture are illustrated in Table-3.

COMPARATIVE EXAMPLE 3

A mixture of low molecular weight and high molecular weight polymerswere prepared by conducting the same procedures as in Example 2 except80 parts of the low molecular weight styrene polymer A-2 and 36 parts ofthe high molecular weight polymer solution A-1 (20 parts as solid) weremixed. The molecular weights and Tg of the resulting polymer mixture areillustrated in Table-3.

EXAMPLE 6

In the preparation of high molecular weight polymer in Example 2, a highmolecular weight polymer B-1 was obtained by conducting the sameprocedures as in Example 2 except 30 parts of xylene were added aftercompleting the bulk polymerization and 0.3 part of tetraethylene glycoldimethacrylate was specially added as a crosslinking agent to thesolution which had been obtained by dissolving 0.1 part of di-t-butylperoxide in 50 parts of xylene. Thereafter the procedures in Example 2were repeated to obtain a mixture of low molecular weight and highmolecular weight polymers. The molecular weights and Tg are illustratedin Table-3.

                                      TABLE 3                                     __________________________________________________________________________                      (2)  (1)                                                    No.               C. Ex-1                                                                            Ex-2                                                                              Ex-3                                                                              Ex-4                                                                              C. Ex-2                                                                            C. Ex-3                                                                            Ex-5                                                                              Ex-6                         __________________________________________________________________________    Low molecular weight polymer (L)                                              Styrene           100  ←                                                                            ←                                                                            ←                                                                            ←                                                                             ←                                                                             90  100                          Butyl acrylate     0   ←                                                                            ←                                                                            ←                                                                            ←                                                                             ←                                                                             10   0                           Polymerization (°C.)                                                                     170  210 190 230 240  210  140 210                          Mn                7200 2100                                                                              3800                                                                              1100                                                                              920  2100 2300                                                                              2100                         Tg (°C.)    87   57  70  45  38  57   47   57                          High molecular weight polymer (H)                                                               A-1  ←                                                                            ←                                                                            ←                                                                            ←                                                                             ←                                                                             ←                                                                            B-1                          Polymer mixture                                                               H/L (as solid)    50/50                                                                              ←                                                                            ←                                                                            ←                                                                            ←                                                                             20/80                                                                              50/50                                                                             ←                       Mn                9700 2800                                                                              4700                                                                              2000                                                                              1600 2500 3700                                                                              2900                         Mz (× 1000) 675  652 663 634 608  154  658 1210                         Mz/Mn              70  233 141 317 380  62   178 417                          Tg (°C.)    71   57  62  50  46  57   51   58                          Duplication characteristics                                                   Fixing ability    Δ                                                                            ⊚                                                                  ◯                                                                     ⊚                                                                  ⊚                                                                   ◯                                                                      ⊚                                                                  ⊚             Contamination of white                                                                          ◯                                                                      ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                      Δ                                                                            ◯                                                                     ◯                background                                                                    Offset resistance ◯                                                                      ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                      X    ◯                                                                     ◯                Blocking resistance                                                                             ⊚                                                                   ⊚                                                                  ⊚                                                                  ◯˜Δ                                                       X    ◯                                                                      ◯˜Δ                                                       ⊚             Variation of electrostatic                                                                      4.8  5.2 5.2 5.7 7.5  12.1 5.2 5.1                          charge                                                                        Dispersibility of coloring                                                                      ◯                                                                      ◯                                                                     ◯                                                                     ◯                                                                     Δ                                                                            X    ◯                                                                     ◯                agent                                                                         __________________________________________________________________________     Note;                                                                         (1) Ex . . . Example                                                          (2) C. Ex . . . Comparative Example                                      

What is claimed is:
 1. An electrophotographic toner which comprises aresin and a coloring agent as a primary ingredient, said resin being anon-crosslinked polymer of a vinyl monomer or a mixture of same, andsaid resin having a number average molecular weight (Mn) of2,000-15,000, a Z average molecular weight (Mz) of not less than 400,000and a ratio of the Z average molecular weight to the number averagemolecular weight (Mz/Mn) of 50-600.
 2. The toner as claimed in claim 1,wherein said resin is a mixture obtained by mixing a high molecularweight polymer with a low molecular weight polymer in a state ofsolution, and said high molecular weight polymer has the Z averagemolecular weight of not less than 400,000 and is prepared by a two steppolymerization wherein the vinyl monomer is polymerized in bulk to aconversion of 30-90% by weight, successively added with a solvent and apolymerization initiator, and the reaction is continued by a solutionpolymerization.
 3. The toner as claimed in claim 2, wherein the mixingratio of the high molecular weight polymer to the low molecular weightpolymer is in a range of 30:70-70:30 as a solid component.
 4. The toneras claimed in claim 2, wherein the high molecular weight polymer isobtained by adding a divinyl compound in an amount of 0.01-1 part byweight per 100 parts by weight of the monomer of said polymer.
 5. Thetoner as claimed in claim 2, wherein the high molecular weight polymercontains 1-15% by weight of methacrylic acid in the monomer of saidpolymer.
 6. The toner as claimed in claim 2, wherein the high molecularweight polymer is initially polymerized the vinyl monomer in bulk to theconversion of 30-90% by weight in the absence of a polymerizationinitiator.
 7. The toner as claimed in claim 2, wherein the low molecularweight polymer is obtained by polymeizing a styrene type vinyl monomerin a state of solution at a temperature of 190°-230° C.
 8. The toner asclaimed in claim 2, wherein said resin is prepared by flashing the mixedsolution of the high molecular weight polymer and the low molecularweight polymer into a vacuum system of 0-200 mmHg.
 9. The toner asclaimed in claim 1, wherein the solvent separated and recovered byflashing is used in the polymerization.
 10. The toner as claimed inclaim 1, wherein the low molecular weight polymer is derived from thevinyl monomer and has Mn of 1,000-5,000, and the mixture of the highmolecular weight polymer with the low molecular weight polymer has Mn of2,000-10,000.